1. Field of the Invention
The present invention relates to a travel control system and method for traveling vehicles. In particular, the present invention relates to centralized control system and method to travel control of the traveling vehicles by a ground controller.
2. Description of the Related Art
In a large scale traveling vehicle system such as an overhead traveling vehicle system, nearly several hundreds of traveling vehicles travel along a travel route, and travel instructions are given to the traveling vehicles from a ground controller for allowing the traveling vehicles to travel autonomously. Each of the traveling vehicles determines its travel route, and implements travel control by determining a distance to a leading traveling vehicle, e.g., using an inter-vehicle distance sensor or communication between the traveling vehicles. Further, the traveling vehicles pass through diverging points and merging points where reliability of the inter-vehicle distance sensor is low, one by one under exclusive control of the ground controller.
In the autonomous traveling system, because of the control delay between the traveling vehicles, it is difficult to allow the leading vehicle and the following vehicle to travel with a short interval therebetween. Specifically, the control delay is a period between the time when the inter-vehicle distance sensor of the following vehicle detects that deceleration of the leading vehicle has been started and the time when deceleration of the following vehicle is started. In the exclusive control, after a blocking request of the traveling vehicle is permitted by the ground controller, a report indicating that the traveling vehicle has passed the diverging point and the merging point is sent to the ground controller. During the time period until blocking is released, the diverging point and the merging point are occupied by one traveling vehicle. Further, in the case where the traveling vehicle determines the travel route autonomously, in the absence of sufficient information regarding the traveling routes of the other vehicles, a traffic jam may occur. In the large scale system, available information is the number of traveling vehicles in each segment, for example. Even if the current traffic jam information is obtained, traffic jam information in the future is not clear. Therefore, it is difficult to determine a particular travel route that can avoid traffic jams.
In view of these points, the inventor studied to implement centralized control for traveling vehicles by a ground controller. According to JP2008-150135A, travel control is implemented by a ground controller to avoid interference between traveling vehicles. However, the JP2008-150135A does not include any disclosure regarding in what manner instructions are provided from the ground controller in a large scale system, and in what manner the traveling vehicles execute the instructions.